Obturator for small arms



Jan. 26, 1965 .1. J. SCANLON, JR 3,166,864

OBTURATOR FOR SMALL ARMS Filed Aug. 1, 1963 INVENTOR. JOHN J. SCANLON, JR.

ATTORNEYS:

3,15%,8645 Patented Jan. 26, 1965 fie 3,166,864 OBTURATOR FGR SMALL ARMS John J. Scanlon, In, Levittown, N..l., assignor to the United States of America as represented by the Secretary of the Army Filed Aug. 1, 1963, Ser. No. 299,437

3 Claims. (Cl. 42-16) (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

This invention relates to the provision of an obturator for an infantry rifle such as the .36 caliber or 7.62 millimeter size and has for an object to provide a device of this sort capable of sealing both the bolt and firing pin against gas leakage past them when an entirely consumable round is used.

It is known that the usual metal cartridge case performs a useful obturating function when it expands under internal pressure and prevents rearward leakage of propellant pressure around the bolt and firing pin. The use of a consumable container for propellant is known to be quite old for well over half a century in separate loading larger caliber artillery weapons. But the situation in those large guns is quite different from what is needed in the .30 caliber rifle. There an obturating pad was carried by the breech closure to prevent gas leakage around it, but such a pad has not been considered appropriate for use on the bolt of the infantry weapon. The primer in those separate loading large guns had an electric or a percussion type primer carried in the breech block and within a metal case. In the smaller gun, no metal case is desired for either the primer or the propellant to obtain maximum lightness in weight. Perhaps two factors have precluded the use of as common a gas seal as an ring on the smaller gun referred to. One is the fact that the breech closing bolt in the .30 caliber rifle usually has a clearance sulficient to cause the O ring to be deformed into such a clearance space resulting in too short a life to make the 0 ring worthwhile. Another is the fact that manufacturers of O ring type packing do not recommend its use where it contacts with gas under the high temperatures and pressures encountered in the firing chamber of the .30 caliber rifle having muzzle velocities above the projectiles from the large low angle fire artillery pieces.

According to this invention two factors hav been introduced to make the use of 0 rings acceptable. One is in the use of an expansion ring subjected to peripheral pressure to compress the ring peripherally when forced into position during assembly so that the clearance both radially inside and outside of the ring may be almost zero whereby there is less tendency for an 0 ring to be deformed or caused to flow into a far smaller clearance space radially outside this ring than that around the bolt and firing pin. Another factor is the cooling of any hot propellant before it is brought in contact with an 0 ring by first providing a guide flange having only a few thousandths of an inch clearance space with the result the hot gas in so thin a cylindrical sheet is considerably cooled by contact with the much cooler metal of the gun. This cooled gas is then further cooled before reaching an O ring by having to pass through a still thinner cylindrical space between some metal part of a gun and the periphery of an expandable ring where the clearance space around it has been said to be much less than a thousandth of an inch. Due to the short time or small fraction of a second during which the very thin sheet of gas is in contact with comparatively cool metal surfaces, it is found from test that the gas is so cooled when brought into contact with an 0 ring, that no visible injury to the O ring was seen.

Referring to the drawing:

FIG. 1 is a longitudinal section showing only the forward end of the bolt and firing pin and without any round of ammunition in the firing chamber.

FIG. 2 shows an expanded position for the duplex ring located on each side of an O ring and before the same has been compressed both longitudinally and diametrically by peripheral pressure.

In FIG. 1 a portion of the barrel 10 of a small arms .30 caliber rifle is shown as having its breech closed by a customary bolt 11, within which a firing pin 12 is slidable for actuating a percussion primer not shown and igniting the propellant, also not shown. The round is of the molded caseless type disclosed in the prior invention 01 Quinlan et al., Serial No. 214,150 filed August 1, 1962, for molded Caseless Small Arms Round. The forward end 13 of the firing pin 12 is rounded as shown for free insertion in the aforementioned round to engage the primer cap and fire said round.

A guide flange 14 on the firing pin 12 performs a two fold function of guiding the firing pin and acting as a heat absorber for any propellant gas that enters between bolt 11 and the reduced end portion 13 of this firing pin. The abrupt change in direction of movement of any hot gas impinging on the front face of flange 14 then again making a bend as it impinges upon the inner surface of bolt 11 and then moves rearward around flange 14, where a further 90 change in direction of movement for a substantial portion of the gas, all assist in cooling the gas before it is brought into contact with the reduced diameter portion 15 of the firing pin 12. Due to the expansive character of ring 18, it is possible that no more of any hot gas may move rearward radially within ring 18 than outside of it. The portion 15 of reduced diameter is shown in FIG. 1 as being made in two parts having a threaded connection 16, the radially outer part as shown as integral with guide flange 14. The radially inner portion is secured to the rear part of the firing pin 12. Any appropriate device to prevent the threaded connection from becoming loose or unthreaded may be used, such for example as a locking pin, not shown but passing through the two parts of the threaded connection. Contiguous the firing pin portion 15 of reduced diameter is an O ring 17 and on each side of the O ring is an expansible ring 18 and 19. One of these expansible rings is shown in FIG. 2 in its expanded or unstressed condition.

Any hot propellant gas which might be expected to pass between the bolt 11 and gun barrel 10 must pass outside guide flange 21 on the forward end of the bolt and forward of the portion 26 of reduced diameter. Guide flange 21 functions in much the same manner as has been mentioned above for flange 14 although of less extent longitudinally. In fact flange 21 is shown as being of minimum axial length and preferably this flange is made longer to better effect cooling of gas which may pass between it and the barrel. An 0 ring 22 is of a size to elfectively seal gas pressure from passing rearward around the bolt when squeezed between the two-turn expandable rings 23 and 24- and contacting both the barrel and bolt tightly enough to effectively seal gas against passing rearwardly as does (3 ring 17. Each of the four expansible metal rings is of beryllium-copper and because of its two convolutions is called a duplex expanding ring. The barrel and bolt are each bevelled or rounded at locations 25 and 26 where these rings must be peripherally compressed to assist in such action.

As shown in FIG. 2 the rings 23 and 24 for the bolt have an outside diameter when unstressed of .474 inch minus .001 of an inch tolerance and an inside diameter of .370 inch-|-.0Ol of an inch, making the radial depth .052 of an inch. The longitudinal width is .028 of an V 3 inch and the pitch .074 of an inch. Each tapered end 25a forms an angle of 30 and its vertex 26a is curved on a radius of .01 of an inch. The angles 27 and 28 are formed to the approximate shape illustrated for the purpose of forming angularly spaced bent portions in the connecting side against which it abuts when compressed. The duplex rings for the firing pin have an outside and inside diameter when unstressed of .304 and .185 of an inchrespectively with the same tolerances making the radial depth .0595 of an inch. When each spring ring is in position ready to be inserted within a recess in a surrounding member the radial depth of each ring is sorelatcd to the size of the reduced diameter portion on which mounted and to the inside diameter of the recess in which it is mounted that in being inserted in such recess it is compressed peripherally an amount to require a snug fit leaving a minimum clearance both inside and outside each ring of no more than about 1 to ten thousandths of an inch or just enough to obtain the good fit required. The purpose of such a good fit is to minimizethe clearance space or crack between the inside and outside to so small an amount that the O ring has so little tendency to flow into the crack that its life is greatlypro longed under the reduced pressure on it.

The ,expansible rings may be inserted on the bolt by having its reduced portion 20 made of separable threaded parts after the manner of what has been shown for the firing pin. Another way is to have the flange 21 provided with a slot forming an angle of about 30 to a normal to the longitudinal axis and through which the ring may be threaded. Either of these expedients is believed to be within the skill of the art for ways of getting the duplex expansible ring in place. 7

Among the advantagesof this invention may be mentioned the provision of both a guide flange to preliminarily cool any hot gas passing in a thin stream outside it, and then further cool that gas in a much thinner stream in passing either inside or outside the duplex expansiblering before it reaches the O ring sealer. The rounded ends '26 of the spring rings have been found adequate to preclude the O ring being cut and the gas pressure longitudinally of these spring rings is believed to avoid any tendency for the O ring to flow in between the ring convolutions at its end contiguous the ring. The extent to which the guide flanges and duplex spring rings reduced the pressure andjternperature of the propellant gas on the 0 ring is not known, but it is known that this invention enables repeated usage of the 0 rings where indicatedsomething that has not previously been accomplished during the two decades and more that consumable rounds have been sought and tried out. The clearance outside the spring rings is necessarily usually more than the clearance radially inside these rings. This means that a major portion of the gas reaching an O ring passed radially inside of it and in doing so is cooled by direct impingement upon two metal walls, that of a forward face of a spring ring and that of the reduced diameter portion. As a result ofthese two impingements the hot gas has changed its direction of travel in two 90 bends, all of which exerts important cooling in addition to that already mentioned.

I claim:

1. In a small arms weapon having a barrel with a metal firing chamber in a rear portion thereof for receiving a consumable round including a projectile secured to molded propellant enabling the round to be loaded as a unit, a metal bolt closing the breech of said chamber and having a metal firing pin slidable Within said bolt for firing a caseless primer within said propellant, the combination therewith of the improvement for reducing leakage of propellant gas rearwardly around bolt and between the bolt and firing pin on firing said round, said improvement including each of said bolt and 'pin having a pertion of reduced diameter, gas sealing means within and forward of said portion of reduced diameter on both the bolt and firing pin, and a heat absorptive guide flange on a forward side of said portion of reduced diameter on both the bolt and firing pin and having no more than a few thousandths of an inch clearance whereby any hot 'gas under pressure is reduced to a thin sheet from which heat is absorbed by metal radially within and outside said sheet, the gas sealing means on each of said bolt and firing pin comprising a deformable plastic 0 ring contiguous the radially inner and outside walls of space around said portion of reduced diameter, and an expansible metal split ring having overlapping tapered end portions and contiguous a high pressure side of each 0 ring, with an expansible ring on the lower pressure side of each 0 ring substantially similar to that on the high pressure side of the same 0 ring, whereby any clearance radially each side of each expansible ring may be reduced to substantially less than .0005 of an inch and the life of the O ring is prolonged when it is not caused to flow into a clearance space of more than such an amount.

2. A combination according to claim 1 in which each expansible ring is of berrylium-copper and of a type having about two convolutions, and the life of an O ring exceeds fifty firings. I

3. In an obtrurating apparatus having a radially outer metal member provided with a cylindrical bore, a cylindrical metal member slidable within said bore and provided with a peripheral recess, and an O ring in said recess, the combination therewith of the improvement enabling saidO ring to possess longer life when used in connection with products of combustion from a propellant, said improvement including said cylindrical metal memher being provided with a guiding end portion adjacent a propellant chamber and having 'a diameter only a few thousandths of an inch smaller than a diameter of said bore, and an expansible metal ring within said recess between said cylindrical guiding end portion and said O ring and having a fit within said bone which is much tighter than that of said guiding end portion and having a peripheral clearance space around said expansiblejring of no more than a few ten thousandths of an inch, whereby a high pressure hot propellant flange entering around said guiding end portion is preliminary cooled by the heat conductive character of said outer 'metal'rnernber and said slidable metal member within said bore, then further cooled by impingement of said flame upon aside of said expansible metal ring, the passa e of only a minor portion of the propellant gas reaching said ring radially outside of said ring and axially thereof where any clearance space is far smaller than that around said guiding end portion, and whereby a major "portion'of the gas impi'n'g ing said 'expansible ring is still further cooled by its impingement upon a base of said recess and then by its passage through a small clearance space radially within said expansible wring between it and a base of-said recess and whereby the gas reaching said 0 ring from the outside of said expansible ring is only a minor portion of that passing said end portion and reaching said expansible ring while a major portion of gas reaching said O'ring has been further cooled'by its direct impingement upon coole-rheat conductive walls followed by two changes in its direction of flow.

References Cited by the Examiner UNITED STATES PATENTS 45,586 12/64 Cleu 89-26 BENJAMIN A. BORCHELT, Primary Examiner.

FRED c. MATTERN, J-R., Examiner. 

1. IN A SMALL ARMS WEAPON HAVING A BARREL WITH A METAL FIRING CHAMBER IN A REAR PORTION THEREOF FOR RECEIVING A CONSUMABLE ROUND INCLUDING A PROJECTILE SECURED TO MOLDED PROPELLANT ENABLING THE ROUND TO BE LOADED AS A UNIT, A METAL BOLT CLOSING THE BREECH OF SAID CHAMBER AND HAVING A METAL FIRING PIN SLIDABLE WITHIN SAID BOLT FOR FIRING A CASELESS PRIMER WITHIN SAID PROPELLANT, THE COMBINATION THEREWITH OF THE IMPROVEMENT FOR REDUCING LEAKAGE OF PROPELLANT GAS REARWARDLY AROUND BOLT AND BETWEEN THE BOLT AND FIRING PIN ON FIRING SAID ROUND, SAID IMPROVEMENT INCLUDING EACH OF SAID BOLT AND PIN HAVING A PORTION OF REDUCED DIAMETER, GAS SEALING MEANS WITHIN AND FORWARD OF SAID PORTION OF REDUCED DIAMETER ON BOTH THE BOLT AND FIRING PIN, AND A HEAT ABSORPTIVE GUIDE FLANGE ON A FORWARD SIDE OF SAID PORTION OF REDUCED DIAMETER ON BOTH THE BOLT AND FIRING PIN AND HAVING NO MORE THAN A FEW THOUSANDTHS OF AN INCH CLEARANCE WHEREBY ANY HOT GAS UNDER PRESSURE IS REDUCED TO A THIN SHEET FROM WHICH HEAT IS ABSORBED BY METAL RADIALLY WITHIN AND OUTSIDE SAID SHEET, THE GAS SEALING MEANS ON EACH OF SAID BOLT, AND FIRING PIN COMPRISING A DEFORMABLE PLASTIC O RING CONTIGUOUS THE RADIALLY INNER AND OUTSIDE WALLS OF SPACE AROUND SAID PORTION OF REDUCED DIAMETER, AND AN EXPANSIBLE METAL SPLIT FING HAVING OVERLAPPING TAPERED END PORTIONS AND CONTIGOUS A HIGH PRESSURE SIDE OF EACH O RING, WITH AN EXPANSIBLE RING ON THE LOWER PRESSURE SIDE OF SAID O RING SUBSTANTIALLY SIMILAR TO THAT ON THE HIGH PRESSURE SIDE OF THE SAME O RING, WHEREBY ANY CLEARANCE RADIALLY EACH SIDE OF EACH EXPANSIBLE RING MAY BE REDUCED TO SUBSTANTIALLY LESS THAN .0005 OF AN INCH AND THE LIFE OF THE O RING IS PROLONGED WHEN IT IS NOT CAUSED TO FLOW INTO A CLEARANCE SPACE OF MORE THAN SUCH AN AMOUNT. 